1. Field of the Invention
The invention pertains to sealing systems for two part fluid handling couplings, particularly couplings wherein one or more of the parts may be under pressure during connection or disconnection. Couplings of this type are often used with hydraulically powered tools wherein different tools may be selectively attached to a common flexible pressurized medium supply hose.
2. Description of the Related Art
Tools and other devices powered by pressurized hydraulic fluid, or compressed air, normally utilize quick connect and disconnect fittings whereby the tools may be quickly attached to a pressurized supply line, or detached therefrom. It is highly desirable that different types and brands of tools be connectable to standard couplings, and the Hydraulic Tool Manufacturers Association (HTMA) has determined standards for couplings for use with its members' products.
Fluid couplings as used with hydraulic tools may be subjected to fluid pressures of 1800 psi or more and as the coupling parts usually incorporate self-sealing valves to prevent the loss of fluid when the coupling parts are disconnected it is not unusual for at least one of the coupling parts to be under pressure when interconnection of the coupling parts is desired. Pressurizing of a fluid circuit may occur because of weight imposed upon an expansible chamber motor within the circuit, or thermal pressurization, or even hose winding or storage may pressurize a hydraulic fluid circuit which would normally be depressurized.
To produce a leak-proof connection between coupling parts, it has been the practice to utilize a conventional O-ring seal located within a recess defined within the passage of the male coupling part which engages a valve sleeve in the female part when full interconnection is achieved. While such conventional use of an O-ring seal is capable of rendering the coupling fluid tight, the disconnection or connection of coupling parts while one or both parts are under pressure causes a short exposure of the O-ring seal to the coupling pressure when the seal is not internally supported which often results in the seal ring being blown from its recess destroying the sealing ability of the coupling. Also, couplings utilizing only conventional O-ring seals often experience the extrusion of the O-ring from its recess into the space between the parts when directly subjected to high pressures, or into the valve seat of the female part, if any misalignment exists during coupling or uncoupling.
To minimize seal ring blow-out and extrusion it has been proposed to employ a stiff and semi-rigid seal ring, rather than a conventional O-ring, in conjunction with the male coupling part recess. By using a semi-rigid seal ring significantly greater resistance to seal blow-out is achieved. One type of semi-rigid seal ring which may be employed in the environment discussed above is disclosed in the assignee's U.S. Pat. No. 4,614,348 wherein a two part seal ring is disclosed having a body of relatively stiff semi-rigid material used in conjunction with a conventional O-ring to prevent fluid bypassing the stiffer seal material.
While the use of a stiff and semi-rigid seal ring does prevent seal ring blow-out during connection and disconnection of the coupling parts, the stiffer and semi-rigid characteristic of the seal ring makes it difficult to acheive effective sealing and this type of seal ring will often permit leakage or seepage. Such leakage may occur because the surface finish engaged by the semi-rigid seal ring is too rough to provide 100% resistance to leakage.
Further, as the valve parts are subjected to numerous connections and disconnections the sealing surfaces of the seal ring may become scratched, particularly in dirty and gritty environments. Also, seals which are formed of stiff and semi-rigid material do not accommodate themselves to manufacturing tolerances as well as softer and more elastic seal rings, and when using a semi-rigid seal ring the presence of maximum tolerances with one coupling part may cause the seal ring to set at such maximum diameter and use of the coupling part containing the seal ring with another female part of a lesser dimension, still within tolerances, may produce spacing which will permit leakage.